The invention relates to a ready-to-install needle bearing with a thin-walled outer ring, which is shaped without cutting and which is provided on both sides with radially inwardly-facing stop rims, with needle rollers rolling between these stop rims on an associated external raceway. The invention also relates to an associated method for the production of the needle bearing according to the invention.
The needle bearing is a cylindrical roller bearing variant with thin, long roller bodies and can be loaded only in the radial direction. Needle bearings have needle rollers with a ratio of diameter:length between 1:2.5 and 1:10. The radial and axial sliding surfaces of the cage or stop rims of the bearing rings take over the axial guidance of the needle rollers. Needle bearings have a very low overall height. Therefore, they are especially well suited for lightweight designs and constructions, in which the installation space in the radial direction is limited.
A ready-to-install needle bearing in the form of a drawn cup needle roller bearing with open ends is known from Catalog 307 “Needle bearings/cylindrical roller bearings” of INA Wälzlager Schaeffler K G, Industriestraβe 1-3, 91072 Herzogenaurach, March 1997. As the associated page 116 of the catalog shows, such a needle bearing is made from a thin-walled outer ring, which is shaped without cutting and which is provided on both sides with radially inwardly-facing stop rims. Between both stop rims there is a needle roller and cage assembly made from needle rollers and a cage, wherein the cage, on one hand, protects the needle rollers from falling inward in the radial direction and, on the other hand, guides these needle rollers in an axis-parallel manner. However, due to its lack of an inner ring, this drawn cup needle roller bearing requires that a supported shaft must be used as an internal raceway. Therefore, it is necessary that such a shaft is hardened and ground in a complicated fashion.
Another ready-to-install needle bearing is distinguished in that the needle rollers are held, in turn, in the axial and radial outward direction in a thin-walled drawn cup, which is shaped without cutting and which forms the external raceway. To also protect the needle rollers from falling in the inward direction, it is known to flange the lateral stop rims of the drawn cup around the ends of the needle rollers. Here it is disadvantageous that, in this arrangement, the ends of the needle rollers must be provided with a journal, which is gripped underneath by the flange edge of the stop rims. Needle rollers configured in this way, however, are very complicated to manufacture. Such a ready-to-install needle bearing is known, for example, from DE 1 894 138 U1. It is also disadvantageous that, in this case, as already discussed above, due to the lack of the inner ring, the shaft to be supported, which presents the internal raceway, must be hardened and ground, in turn, in a complicated fashion. Due to the lack of the needle roller cage, an increased basic load rating is indeed possible, but the intricate holding of the needle rollers with their tapering projections by the flange edges of the stop rims makes the assembly of such a bearing considerably more difficult.
Now, in this context, a needle bearing has indeed become known from DE 928 020, which appears, at first glance, to stand in direct relation with the solution according to the invention. In FIGS. 1 and 2, a needle bearing is shown, which is made from two bearing rings, which both have inwardly-facing and outwardly-facing rims. Apart from the fact that the needle bearing according to DE 928 020 is manufactured using a cutting method and not in a method without cutting, from the description it emerges that the rims are not equal. On page 2 in column 1, line 24ff. it is listed that, with reference to FIG. 1, at first the needles 1 are embedded in the inner ring 4 provided with the rims 2 and 3 with the help of a stiff grease and the previously heated outer ring 5 is pushed over from left to right via the needles. This method of production is allowed, in particular, in that only the rim 6 of the outer ring is constructed normally, while the rim 7 has a height that is so low that it allows the outer ring 5 expanded by heating to be pushed over the rim and creates a tight connection of the components 1, 4, and 5 after its cooling. This means that this shortened rim 7 has a height that is so low that a radial overlap between the bearing needle 1 and rim 7 is realized only in the μm range. Uncontrolled heating of the bearing could also lead to the result that no axial contact of the bearing needles 1 on the rim 7 of the outer ring is possible.